JP2019039029A - Cu-CONTAINING STEEL SHEET - Google Patents

Abstract

To provide a Cu-containing steel that is prevented generation of artifact CuS and has excellent corrosion resistance for a steel sheet containing Cu.SOLUTION: A Cu-containing steel sheet contains, by mass, 0.001% or more Cu, and at least Cu-clusters with circle equivalent diameters of 1-1000nm are present in the steel.SELECTED DRAWING: None

Description

  The present invention relates to a Cu-added steel plate, in particular, a Cu-added steel plate which is prevented from generating an artifact and is excellent in corrosion resistance.

Metallic materials, in particular steel materials, are required for steel materials by controlling the types of inclusions and precipitates present in the material matrix and the shape, size, etc. of aspect ratio, etc. by minor additive elements and various heat treatments. Control of strength and characteristics is widely practiced.
Therefore, it is important to observe inclusions and / or precipitates, and to measure the components and amounts thereof in order to analyze the quality control of the steel material and the manufacturing process.

  In order to observe inclusions and precipitates by SEM, etc., it is necessary to expose inclusions and precipitates in a state of being buried in the matrix on the observation surface, and conventionally, electrolysis is carried out in various electrolyte solutions. Inclusions and precipitates are exposed on the surface of the sample to allow observation.

  In recent years, with advances in steel material manufacturing technology, the types of inclusions and precipitates have diversified, and fine dispersion has progressed, and in observation, only the matrix (Fe) is selectively dissolved and the inclusions are interposed. With regard to substances and precipitates, even if they are fine particles, there is a demand for an electrolytic solution which is reliably held on the observation surface and does not dissolve.

  In addition, when identifying and quantitatively analyzing these inclusions and precipitates, similarly, the matrix of the steel sample is dissolved in the electrolyte solution, and the inclusions and precipitates are recovered as electrolytic residue, and this is identified Quantitative analysis has been conducted.

  In the case of this quantitative analysis, only the matrix portion of the steel material is efficiently electrolyzed, and the Fe content is reliably dissolved and held in the electrolytic solution, and the portion corresponding to other inclusions and precipitates is electrolyzed. It is required to be able to be reliably recovered as a residue.

Patent Document 1 describes an electrolytic solution composition for a steel sample, and an analysis method of inclusions and precipitates using the same.
This electrolytic solution composition is dissolved by the addition of alkaline triethanolamine, even though the conventional electrolytic solution is often acidic, even if it is a minute inclusion or precipitate, it is dissolved. This makes it difficult for particles of these inclusions and precipitates to easily remain on the surface of the steel sample, and after the steel sample is taken out of the electrolytic solution and dried, observation and analysis by SEM or the like are possible as it is.

Patent Document 2 discloses an invention related to a non-aqueous solvent-based electrolytic solution for extraction of inclusions and precipitates in steel samples and an electrolytic extraction method of steel samples using the same.
This electrolyte contains maleic anhydride, tetramethyl ammonium chloride and methanol in a predetermined ratio, and is an electrolyte excellent in the ability to electrolyze a large amount of steel samples at one time, and is contained in the solution. Maleic anhydride has the feature of preventing complex precipitation of iron chelates.

On the other hand, Patent Document 3 is not a technology for steel samples, but in order to precipitate and separate arsenic as an impurity element in a copper-containing mineral from a copper ion, triethylenetetramine (as a suspension inhibitor for arsenic minerals). Techniques using TETA) and ethylenediaminetetraacetic acid (EDTA) are disclosed.

In order to observe inclusions and precipitates in a steel sample in situ by SEM or the like, the sample is electrolyzed, and the Fe component constituting the matrix is held in the electrolytic solution with a Fe ion chelating agent, inclusions It electrolyzes so that a deposit may remain on the sample surface.
On the other hand, in the case of quantitative analysis of inclusions and precipitates, the Fe component of the matrix is held in the electrolytic solution by a chelating agent, and an electrolytic solution which does not dissolve inclusions and precipitates separated from the sample by electrolysis is used. These are recovered as electrolytic residues, and the residues are identified and quantitatively analyzed.
Therefore, with regard to an electrolytic solution for the purpose of recovery of residues for identification and quantitative analysis of inclusions and precipitates, it is mainly intended that the Fe content can be maintained as a chelate complex in the electrolytic solution, No special consideration has been given to contamination of inclusions and precipitates in the solution.

JP, 2002-303620, A JP 2000-137015 A JP, 2011-156521, A

During metal compound analysis in steel materials due to electrolytic corrosion and the like in conventional non-aqueous solvent-based electrolytes, fine particles of inclusions and precipitates, in particular, various metal compounds, in particular, the surface layer of MnS, other than electrolytic operation The phenomenon of unknown cause that CuS concentration higher than the content measured by the means was observed was observed in some cases. For this reason, MnS particles may be detected as CuS (Artifact CuS).
In particular, in a Cu-containing steel sheet, in the conventional analysis method of sulfide, Cu attacked MnS, and MnS was disguised as if it is CuS, so that clear analysis could not be performed.

The inventors of the present invention examined the cause in detail, and as a result, when a metal ion (Cu 2+) having a small solubility product Ksp is formed in the electrolytic solution by electrolytic operation, a metal sulfide (MnS)
It has been found that metal ions (Mn 2+) with large solubility product Ksp are exchanged with metal ions (Cu 2+) with small solubility product Ksp on the surface of. In addition, it was found that such metal ion substitution on the surface of sulfide easily proceeds at ordinary temperature and pressure, and also in an aqueous solution or non-aqueous solvent.

  As a result, inclusions and precipitates originally present as MnS in the steel sample will be observed as CuS as long as the surface is observed, and Cu ions in the electrolytic solution may be observed on the surface of MnS. Even if mass analysis is carried out from the residue by exchanging CuS due to a thickness of several tens of nm (1 to 100 nm), CuS occupies a considerable portion of the volume in the case of fine particles. Therefore, accurate quantification was impossible.

Then, the subject which this invention tends to solve is the following.
-It is an object of the present invention to provide a Cu-added steel having excellent corrosion resistance, in which a Cu-containing steel plate is prevented from generating an artifact (symmetry) CuS.

The present inventors diligently studied methods for solving the above problems.
As a result, if it is found that a metal (attack metal) that forms an artifact (simulated metal) metal sulfide does not exist in the solvent-based electrolyte solution, it is possible to supplement such attack metal from the finding that the substitution phenomenon does not occur. I came to my thoughts. That is, a free attack metal in the electrolytic solution can be obtained by adding a drug (such as a chelating agent) that selectively captures the metal (attack metal) that forms the artifact (simulated metal) metal sulfide in the solvent-based electrolytic solution. It is thought that the decrease of the artifact metal sulfide is not generated.

For example, Cu ions dissolved out of steel samples etc. are held in the electrolytic solution by a Cu ion chelating agent so as not to attack MnS on the surface of the steel sample for surface observation, or identification / quantification of inclusions or precipitates Similarly, in the electrolytic operation for analysis, Cu ion is held as a chelate complex in the electrolytic solution as a chelate complex by the Cu chelating agent in the residue for quantitative analysis prepared from inclusions or precipitates. In addition, by preventing the CuS from being mixed, it is possible to observe inclusions and precipitates in the steel sample for surface observation as it is in the original form, and in the electrolytic residue to be analyzed. And that it is possible to correctly identify and quantify only elements originating from inclusions and precipitates originally contained in the steel sample without containing CuS etc. derived from Cu ions dissolved out from the matrix of the sample etc. Found it was.

By this analysis method,
(1) It is possible to provide a Cu-added steel sheet characterized by containing at least 0.001% by mass of Cu and containing at least a Cu cluster of 1 to 1000 nm as an equivalent circle diameter in the steel. .
(2) In addition, it is possible to provide the Cu-added steel sheet according to (1) described in (1) characterized by containing, by mass%, Mn: 0.001% or more and S: 0.0001% or more.
(3) The Cu according to any one of (1) to (2), wherein the ratio of SasCuS (S producing CuS) to Sas MnS (S producing MnS) is 10% or less. It becomes possible to provide an additive steel plate.
(4) Furthermore, the corrosion resistance of the Cu-containing steel sheet is improved from that of the non-Cu-containing steel sheet by the Cu clusters dispersed in the steel sheet at a distance of at least two with a circle equivalent diameter of 1 to 1000 nm. It becomes possible to provide the Cu addition steel plate of a statement (1)-(3) characterized by things.
(5) Triethylenetetramine (TETA) Inclusion particles are contained in the inclusion particle portion of the steel plate electrolyzed by the electrolytic solution (5% TETA) composed of 5% by volume + 1% by mass tetramethylammonium chloride (TMAC) It becomes possible to provide the Cu-added steel sheet as described in (1) to (4) characterized in that it contains Mn and S, but the Cu component is not contained in inclusions.

-It becomes possible to provide a Cu-added steel in which the generation of the artifact CuS is prevented in a Cu-containing steel plate.
-Surprisingly, in the Cu-added steel in which the generation of the artifact CuS is prevented, at least a 1-1000 nm Cu cluster with an equivalent circle diameter is present, thereby improving the corrosion resistance of the non-Cu-containing steel plate Do.
In the surface analysis of the extracted metal fine particles, fine particles of MnS or FeS are not mistaken as CuS as in the prior art, and the true form (size, component) of the metal sulfide can be known, and further, The content of metal sulfide in the steel material can also be accurately grasped.
In addition, it becomes possible to observe inclusions or precipitates etc. exposed on the steel sheet surface by electrolysis operation with components and forms originally present in steel samples, and inclusions and precipitation from analysis of electrolytic residue In the case of quantitative analysis of waste components, accurate quantitative analysis can be performed without the influence of Cu etc. mixed from the electrolytic solution, so structural observation of steel samples and identification of inclusions or precipitates in steel samples -It contributes to the improvement of the accuracy of quantitative analysis.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows an example of a sketch of an electrolytic device using an electrolytic solution according to the present invention. It is a graph which shows the SEM photograph and the element concentration of the vicinity of the inclusion of the electro-polished steel sample. It is a graph which shows the SEM photograph and the element concentration of the vicinity of the inclusion of the iron and steel sample mirror-polished. It is a graph which shows the analysis result of the electrolysis residue of a steel sample.

Extraction of metal compound particles in a metal material (Cu-added steel plate) for observation of the Cu-added steel plate of the present invention will be described. Specifically, by etching the metal material in the electrolyte solution, the matrix (Fe and the like) is selectively dissolved to expose metal compound particles such as inclusions and precipitates contained in the metal material on the sample surface. . Thereby, the metal compound particles can be brought into an observable state.
As a method of extracting fine particles in the metal sample, for example, acid decomposition method which dissolves iron matrix of steel sample in acid solution, halogen dissolution which dissolves iron matrix of steel sample in iodine methanol mixed solution or bromine methanol mixed solution A non-aqueous solvent-based constant current electrolysis method or a non-aqueous solvent-based constant potential electrolysis (SPEED: Selective Potentiostatic Etching by Electrolytic Dissolution Method) method can be used. Among these, the SPEED method using a non-aqueous solvent is preferable because when the fine particles are dispersed in the solvent, the change in the composition or the size does not easily occur and even the unstable fine particles can be extracted stably. In the present embodiment, an evaluation method of fine particles in steel material by non-aqueous solvent based constant potential electrolysis method (SPEED method) will be described as an example with reference to FIG. 1, but the extraction method in the present invention is It is not limited to the SPEED method, and the metal material is not limited to the steel material.

  First, the metal sample 4 is processed into a size of, for example, 20 mm × 40 mm × 2 mm, and oxide films and the like such as scale on the surface layer are removed by chemical polishing or mechanical polishing to release the metal layer. . On the contrary, when analyzing the fine particles contained in the oxide film layer, it is left as it is.

  The metal sample is then electrolyzed using the SPEED method. Specifically, the electrolytic cell 10 is filled with the electrolytic solution 9, and the metal sample 4 is immersed in the electrolytic solution 9 to bring the reference electrode 7 into contact with the metal sample 4. The platinum electrode 6 and the metal sample 4 are connected to the electrolytic device 8. In general, when the above-mentioned electrolysis method is used, the electrolysis potential of fine particles in steel such as precipitates has a high electrolysis potential as compared with the electrolysis potential of the metal portion which becomes the matrix of the metal sample 4. Therefore, it is possible to selectively dissolve only the matrix by setting the voltage between the electrolysis potentials for dissolving the matrix of the metal sample 4 using the electrolytic device 8 and not dissolving the fine particles such as precipitates. It becomes. Inclusions or precipitates 5 float on the surface of the sample on which Fe in the surface matrix portion is electrolytically eluted, and it is in a state suitable for observation by SEM or the like. Further, electrolysis may be continued to separate inclusions and precipitates from the surface of the sample, to be collected as the electrolytic residue 11, filtered and separated from the electrolytic solution, and used for identification and quantitative analysis.

An electrolytic solution for observing a metallic material according to the present invention, that is, to electrolyze a Fe matrix on the surface to observe inclusions and precipitates, or to quantitatively analyze inclusions and precipitates. The electrolytic solution used for the electrolysis to electrolyze and recover the residue is preferably
(1) complexing agents for Fe ions,
(2) An electrolyte for securing conductivity to the electrolyte,
(3) A solvent for holding the formed complex such as Fe in a liquid,
including.

  As a complexing agent for the Fe ion, one or more may be selected from acetylacetone, maleic anhydride, maleic acid, triethanolamine, salicylic acid and methyl salicylate.

  As the electrolyte, one or more types can be selected from tetramethyl ammonium chloride (TMAC), sodium chloride (NaCl), and lithium chloride (LiCl).

  The solvent needs to be capable of holding various complex-forming agents or complexes of these with Fe in a dissolved state, and may be a non-aqueous solvent. In aqueous electrolytes, various precipitates are decomposed even at relatively low electrolysis voltage (for example -300mV or less), whereas in non-aqueous electrolytes, stable electrolysis area is wide, and superalloys, high alloys, stainless steel to carbon It can be applied to almost all steel materials up to steel. When a non-aqueous electrolytic solution is used, mainly, only the dissolution of the matrix and the (complexation) reaction between the dissolved Fe ions and the chelating agent occur, and the inclusion or precipitate 5 is not dissolved, and the matrix Three-dimensional observation and analysis in the "in situ" state can be performed above. As the non-aqueous solvent, a compound which facilitates electrolysis and dissolves a complexable organic compound and a supporting electrolyte is suitable. For example, lower alcohol such as methanol, ethanol or isopropyl alcohol is used. Can. Methanol, or ethanol, or mixtures thereof can be selected. Further, any solvent having polarity (dipolar moment etc.) equal to or higher than these alcohols can be used.

  In the conventional constant potential electrolysis method, as an electrolytic solution, for example, 10% by mass acetylacetone (hereinafter referred to as “AA”)-1% by mass tetramethylammonium chloride (hereinafter referred to as “TMAC”)-methanol solution, or 10% by mass Maleic anhydride-2% by weight TMAC-methanol solution is used. In these electrolytic solutions, the electrolytically eluted Fe forms a complex, and the generated Fe complex is preferably used from the viewpoint of dissolving in the electrolytic solution, and therefore, it is widely used.

In the electrolytic solution, metals other than the matrix (Fe) may elute, although the amount is relatively small compared to the matrix (Fe). When the solubility product Ksp of the eluted metal is small and the inclusions or precipitates 5 and the electrolytic residue 11 contain a metal compound of a metal having a large solubility product Ksp, a metal ion having a large solubility product Ksp (for example, The inventors have found that Mn 2+) is replaced by a metal ion with a small solubility product Ksp (eg Cu 2+). This substitution is considered to proceed easily when the solubility product Ksp has a difference of about 10 digits (10 ¹⁰ ). When there is a difference of about 20 digits (10 ²⁰ ) in the solubility product Ksp, it is considered that the substitution proceeds more easily.

For example, when MnS is present on the surface of the steel sample or in the electrolyte residue, the sulfide of Cu ions dissolved in the electrolyte has a difference in solubility product Ksp with MnS of 23 digits, so While attacking and ionizing Mn and driving it out into the electrolytic solution, it remains as CuS on the MnS surface. That is, inclusions and precipitates originally present as MnS in the Cu-containing steel sample will be observed as CuS as long as the surface is observed. Also, in the case of fine particles, even if mass analysis is performed from the residue by substituting CuS due to Cu ions in the electrolytic solution on the surface of MnS to a thickness of about several tens of nm (1 to 100 nm) MnS In this case, since CuS occupies a considerable part of the volume, accurate quantification becomes impossible. Such a phenomenon in which the metal near the surface is replaced may be referred to as an artifact in the present specification.

  As an attack metal M 'which is likely to cause an artifact, Cu is remarkable because of its content and low solubility product Ksp. Cu can easily attack the surface of MnS or FeS having a solubility product Ksp difference of about 20 digits with respect to a Cu compound, and can cause an artifact.

  Crown ethers are available as agents for forming complexes containing such attack metals M '. Crown ethers are cyclic polyethers (with several ether units connected), and the size of the cyclic holes can be changed. Therefore, depending on the attack metal species M ', a crown ether having an appropriate hole can be prepared, whereby only the attack metal species M' can be selectively captured.

  The agent for forming a complex containing an attack metal M 'may contain any one or more of polyethyleneamines, ethylenediaminetetraacetic acid, and cyclohexanediaminetetraacetic acid. They act as chelating agents and capture the attack metal M '. Examples of polyethyleneamines include triethylenetetramine (TETA), penicillamine, pentaethylenehexamine and the like. In particular, a chelating agent such as triethylenetetramine has high selectivity to Cu ions, and exhibits a particularly high capturing effect when the attack metal M 'is Cu.

  The attack metal M 'is trapped to form a complex of the attack metal M'. The complex of the attack metal M 'is kept in solution in the above-mentioned solvent. Therefore, even if the metal compound MxAy having a large difference in solubility product Ksp, attack metal M 'can freely substitute for metal M on the surface of metal compound MxAy (that is, artifact). Can not. In other words, the generation of M'x'Ay 'is suppressed.

  The metal material in the present invention may be a steel material. The iron and steel material refers to a material containing iron as a main component, and may contain a trace amount of carbon.

  When the electrolytic solution after etching is passed through a filter and metal compound particles are extracted as a collected residue, the filter may be a tetrafluoroethylene resin filter. For filters that filter inclusions or precipitates 5 or residue 11 from the electrolyte for identification and quantitative analysis of inclusions or precipitates 5 or residues 11, a conventionally used Nucripore filter (manufactured by GE) However, it is difficult to dissolve and damage the residue. In particular, when the chelating agent contains triethylenetetramine, filter damage is significant. If it is a filter made of tetrafluoroethylene resin, even if the chelating agent contains triethylenetetramine, it is preferable because the dissolution damage is small.

It is also provided that the metal compound particles extracted by the above method are analyzed. The analysis may be surface elemental analysis of metal compound particles.
According to the present invention, an attack metal (such as Cu ion) which attacks and substitutes constituent elements of inclusions and precipitates in the electrolytic solution is selectively retained as a complex, and dissolved stably in the electrolytic solution. If components to be maintained are added, inclusions and precipitates can be observed in the form originally present in the steel sample in surface observation of the sample, and in identification and quantitative analysis of inclusions and precipitates. The above-mentioned Cu ion etc. are mixed in the electrolysis residue which is the analysis object, and the identification and quantitative analysis accuracy of inclusions and precipitates are not lowered. For example, by the surface analysis of the extracted metal fine particles according to the present invention, it is possible to know the true appearance (size, component) of the metal sulfide without actually recognizing the fine particles of MnS or FeS as CuS. Furthermore, the content of metal sulfide in the steel material can also be accurately grasped.

  The above-mentioned electrolytic solution may contain a particle dispersing agent such as SDS as necessary as a component other than the agent (Cu ion chelating agent etc.) selectively capturing the above-mentioned attack metal (Cu ion etc.).

When the matrix was observed with an electromagnetic microscope, it was found that in the Cu-added steel sheet of the present invention, the formation of an artifact due to Cu is prevented, and Cu is solid-soluted in the steel. Specifically, it was found that at least a 1-1000 nm Cu cluster with an equivalent circle diameter was present in the steel. In addition, Cu cluster means the state in which pure Cu existed locally in a matrix in steel in the matrix, and the form is not ask | required. This is because the Cu cluster is formed by Cu in solid solution at high temperature in the Cu-added steel plate through crystallization and the like in the subsequent cooling step, and the form of the Cu cluster fluctuates depending on the cooling condition and the like. . The Cu cluster can be observed with an electron microscope or the like.
Conventionally, when a steel plate having a Cu cluster is electrolyzed, Cu attacks MnS or the like, and it looks as if MnS is CuS (pseudo-control), and as a result, the material balance of each element including Cu It is conceivable that the accuracy of the In particular, when a Cu cluster is not formed in a Cu-added steel sheet, it is considered to be present as an unstable Cu element, so that the simulation to CuS proceeds and the accuracy of material balance decreases. On the other hand, in the above-mentioned electrolysis method, the simulation by Cu is suppressed and as a result, the accuracy of material balance of each element including Cu improves.

Surprisingly, the presence of Cu clusters is considered to have the effect of improving the corrosion resistance of the Cu-added steel sheet. Cu has the property of forming fine precipitates to enhance the strength of the steel, which is considered to affect corrosion resistance. However, in the case of a Cu-added steel sheet, when a Cu cluster is not formed, it tends to be present as an unstable Cu element, and it is therefore considered that the corrosion resistance is lowered. Moreover, as for a non-Cu containing steel plate, naturally Cu cluster does not exist. A Cu-added steel plate in which a Cu cluster having a circle equivalent diameter of at least 1 to 1000 nm is present is superior in corrosion resistance to a non-Cu-containing steel plate in which no Cu cluster is present. The contact resistance can be evaluated by suspending the sample in the air at 50 ° C. and humidity 98% and observing the surface condition after 7 days, and the like. With a Cu cluster smaller than 1 nm in diameter with a circle equivalent diameter, there is a possibility that the corrosion resistance can not be sufficiently improved. A Cu cluster having a circle equivalent diameter of more than 1000 nm in diameter may cause uneven dispersion of additive elements such as Cu, which may cause a disadvantage based on the inhomogeneity.
In particular, when at least two or more Cu clusters having a circle equivalent diameter of 1 to 1000 nm diameter exist and they are separated and dispersed, the corrosion resistance is further improved.

Further, in the Cu-added steel sheet of the present invention, the ratio of SasCuS (S producing CuS) to Sas MnS (S producing MnS) may be 10% or less.
In the analysis by the conventional electrolytic method, Cu attacked MnS etc. and it appeared as if MnS was CuS (fake mechanism). However, in the Cu-added steel sheet according to the present invention, it has been found that the simulation by Cu is suppressed. That is, the ratio of SasCuS (S producing CuS) to SasMnS (S producing MnS) is a value lower than that of the conventional one and may be 10% or less. This ratio is considered to be inversely related to the presence of the Cu cluster. That is, the fact that the ratio of SasCuS is small leads to the suppression of the simulation by Cu, and as a result, the existence of the originally existing Cu cluster can be more easily confirmed.

  In addition, the Cu addition steel plate of this invention contains Cu as the premise. The Cu content is 0.001% by mass or more. Cu has the effect of forming fine precipitates to increase the strength of the steel, which is considered to be related to the above-mentioned action of improving the corrosion resistance by the Cu cluster.

  Further, the Cu-added steel sheet of the present invention may contain Mn: 0.001% or more and S: 0.0001% or more.

  S is an unavoidable impurity element contained in the steel. If the S content is excessive, S is present in the steel in a solid solution state, and the steel becomes brittle during hot rolling. Therefore, the lower the S amount, the better, so the upper limit may be 0.01%. However, since the excessive reduction leads to an increase in raw materials and refining costs, the lower limit is made 0.0001.

  Mn is one of the important elements in the present invention because Mn reacts with S to form a sulfide. If the Mn content is less than 0.001%, the steel sheet may be embrittled during hot rolling, so the lower limit of the Mn content may be 0.001%. Even if Mn is added in excess, the effect is saturated, so the upper limit of the Mn content may be 2.0% in consideration of cost effectiveness and the like.

  The Cu-added steel sheet of the present invention is a part of inclusion particles of a steel sheet electrolyzed by an electrolytic solution (5% TETA) composed of 5% by volume of triethylenetetramine (TETA) + 1% by mass of tetramethylammonium chloride (TMAC) The inclusion particles may contain Mn and S, while the Cu component may not be included in the inclusions.

  Hereinafter, the present invention will be described through examples. However, the present invention should not be construed as being limited to the following examples.

  The inclusions or precipitates in the steel sample according to the present invention were observed by the following electrolytic solution and electrolytic method. As a control example, a conventional electrolytic solution (4% MS) containing 4% by mass of methyl salicylate + 1% by mass of salicylic acid + 1% by mass of tetramethylammonium chloride (TMAC) capable of recovering conventionally known sulfide-based inclusions as a residue Were used to observe inclusions or precipitates of the same steel sample that had been electrolyzed. As an electrolyte for analyzing a steel sample according to the present invention, an electrolyte (5% TETA) of triethylenetetramine (TETA) 5% by volume + 1% by mass tetramethylammonium chloride (TMAC) was used. The solvent used was methanol.

The results are shown in FIG.
Fig. 2a is a steel sample whose surface is electrolyzed by an electrolyte (5% TETA), and Fig. 2b is an EDS photograph of a steel sample whose surface is electrolyzed using a conventional electrolyte (4% MS). The graph of Cu density | concentration measured by was superimposed and shown. Before electrolysis, the steel sample was subjected to mirror polishing in advance to remove surface impurities.
Below each scanning electron micrograph, what was extracted and described only the said Cu density | concentration graph was carried out similarly.

  Since the height of the value in the graph (Cu concentration) is relative, when electrolyzing with an electrolytic solution (5% TETA), there is no difference between the precipitated particles and the Fe matrix portion. As can be seen, when the Cu concentration is measured by electrolysis in the conventional electrolytic solution (4% MS) shown in FIG. 2b, it can be seen that the Cu concentration is increased in the precipitated particle portion.

The inventors of the present invention performed mirror analysis only on the steel samples used in the above-described Examples and Comparative Examples, and subjected them to elemental analysis.
The results are shown in FIG. In the same figure, SEM is a scanning electron micrograph of the inclusion particle existence part. Elemental analysis was performed on this particle and its vicinity.
As a result, in the portion of the inclusion particles, the values of the graph of Mn and S are rising, and it can be confirmed that the inclusion particles contain Mn and S, that is, specifically, MnS.
On the other hand, it was also confirmed that the Cu component did not have a peak and was not contained in inclusions.

  From the results described above, when a steel sample is electrolyzed using a conventional electrolytic solution (4% MS), and observation by SEM or the like and microanalysis by EDS are performed, MnS originally observed in the steel material is electrolytic It was found that by immersing in a liquid (4% MS), at least the surface of MnS was contaminated with CuS, causing a failure observed as CuS.

On the other hand, when electrolytic solution (5% TETA) is used, MnS is retained as MnS without causing the above-mentioned problems. Therefore, observation by SEM or micro analysis by EDS is also possible in steel samples. Since it can be observed in the state originally present in the steel, it can greatly contribute to the improvement of the analysis accuracy of the steel sample.
As a result, it is possible to provide a Cu-added steel in which the formation of the artifact CuS is prevented in a Cu-containing steel plate.

  Quantitative analysis of inclusions or precipitates in steel samples was performed by electrolysis using an electrolytic solution (including TETA). As a control example, a steel sample electrolyzed using a conventional electrolytic solution (4% MS) was prepared.

As a steel sample, a steel material containing 0.4 mass% Cu was solutionized by heat treatment at 1350 ° C. for 30 minutes, and then a sample quenched in water was used.
The following three types of electrolyte solutions were prepared.
(1) 4% MS: 4% by mass capable of recovering conventionally known sulfide inclusions as a residue
Methyl salicylate + 1 wt% salicylic acid + 1 wt% tetramethyl ammonium chloride (TMAC) as a control.
(2) 4% MS + 5% TETA: A solution obtained by adding 5 vol% of triethylenetetramine (TETA) which forms a complex with Cu ion to 4% MS of (1).
(3) 5% TETA: triethylenetetramine (TETA) 5% by volume (TETA) 5% by volume + 1% by mass tetramethylammonium chloride (TMAC) electrolyte solution.
The solvent was methanol in any of (1) to (3).

  For each electrolytic solution, the sample was electrolyzed by about 1 g equivalent, the contents of Mn and Cu contained in the obtained electrolytic residue were quantified by wet chemical analysis, and the content contained in a 1 g steel sample was calculated.

The results are shown in FIG.
In the figure, the three band graphs show Mn and Cu detected in the electrolytic residue, respectively, in% units, and from the left, (1) in the conventional electrolytic solution (4% MS) In the case of electrolysis, (2) in the case of electrolysis with an electrolyte (4% MS + 5% TETA) to which 5 vol% of TETA is added to the conventional electrolyte, (3) electrolysis with an electrolyte to which 5 vol% TETA (5% TETA) is added If it shows, In each case, electrolysis was performed using the Pt electrode as a cathode.

  In addition, when the steel sample adopted in the example was mirror-polished and the distribution of the component elements was analyzed by EDS etc., most of Cu contained in the sample is in solid solution in the matrix part of the sample, CuS or It has been confirmed that it does not exist in the form of sulfide such as CuS.

  Nevertheless, in the electrolysis with the conventional electrolytic solution (4% MS) shown in (1) of FIG. 4, the Mn concentration is 143 ppm from the electrolytic residue in which the sulfide in the steel sample is considered to be the main component Concentration of Cu (334 ppm) was measured.

The graph shown in (2) shows the concentrations of Mn and Cu measured from the electrolytic residue when electrolyzed with the electrolytic solution (4% MS + 5% TETA) to which 5 vol% of triethylenetetramine is added.
In this case, the Cu component in the electrolytic residue is reduced to 62 ppm.

Moreover, (3) shows the measured value in the case of triethylenetetramine 5 volume% electrolyte solution (5% TETA).
The Cu concentration measured from the electrolytic residue decreased to 12 ppm.

In addition, in the electrolyte solution which added triethylene tetramine to the electrolyte solution, since the conventional Nucle pore filter will melt | dissolve, it is necessary to use a filter insoluble in the said electrolyte solution.
The present inventors have found that the dissolution phenomenon of the filter can be prevented by employing a polyfluoroethylene filter.

That is, if a steel sample is electrolyzed using an electrolytic solution containing TETA, the chemical analysis accuracy of the residue is improved, and it becomes possible to accurately identify and quantify inclusions and precipitates present in the sample.
As a result, it is possible to provide a Cu-added steel in which the formation of the artifact CuS is prevented in a Cu-containing steel plate.

Si: 3.3%, Mn: 0.10%, Al: 0.8%, N: 0.002%, S: 0.009% and Cu: 1.2%, the balance being Fe and unavoidable Steel made of chemical impurities was melted, and a billet (slab) was produced from this steel. Next, the billet was heated at 1100 ° C. for 60 minutes and immediately hot rolled to obtain a hot-rolled sheet having a thickness of 2.0 mm. Thereafter, the hot-rolled sheet is subjected to hot-rolled sheet annealing at 1020 ° C. for 60 seconds, pickled, and cold-rolled once to obtain a cold-rolled sheet having a thickness of 0.30 mm. Subsequently, the cold rolled sheet was subjected to finish annealing at 900 ° C. for 45 seconds.
At this time, the number of stages of cooling between finishing and winding of the hot rolling was changed as shown in Table 1.
By analyzing the Cu analysis in the obtained steel sheet by the analysis method based on Example 1, by grasping the conditions in which the formation of the artifact (symmetry) CuS is prevented, it could not be grasped by the conventional Cu analysis method It became possible to find conditions under which the formation of artifact CuS was prevented. In addition, when the Cu dispersion degree of the steel plate of this invention example was observed with the electron microscope, it was confirmed that 1-1000 nm Cu cluster by an equivalent circle diameter exists in steel. Moreover, it has also been confirmed that these steels have excellent corrosion resistance.
With respect to the contact resistance, the sample was suspended in an atmosphere of 50 ° C. and a humidity of 98%, and the surface condition after 7 days was evaluated. In the case of failure, rust was generated, and in the case of good, generation of rust was not observed. In some cases, some rusting was observed.

  By electrolysis of a steel sample using a TETA 5% electrolytic solution, it becomes possible to observe inclusions and precipitates in the sample in the form as they originally exist in the sample and, at the same time, of these inclusions and precipitates Also in the chemical analysis, it is possible to eliminate the contamination caused by the contamination by Cu or the like, and to improve the accuracy of the chemical analysis. As a result, it is possible to provide a Cu-added steel in which the formation of the artifact CuS is prevented in a Cu-containing steel plate.

Claims (5)

  A Cu-added steel sheet characterized by containing at least 0.001% by mass of Cu and containing at least a Cu cluster of 1 to 1000 nm as an equivalent circle diameter in the steel.   The Cu-added steel sheet according to claim 1, containing, by mass%, Mn: 0.001% or more and S: 0.0001% or more.   The Cu-added steel sheet according to claim 1 or 2, wherein the ratio of SasCuS (S producing CuS) to SasMnS (S producing MnS) is 10% or less.   The corrosion resistance of the Cu-containing steel plate is improved from that of the non-Cu-containing steel plate by the Cu clusters dispersed in the steel plate with a circle equivalent diameter and separated by at least two with a diameter of 1 to 1000 nm. The Cu-added steel plate according to any one of Items 1 to 3.   In the inclusion particles of the steel plate electrolyzed with an electrolytic solution (5% TETA) of triethylenetetramine (TETA) 5% by volume + 1% by mass tetramethylammonium chloride (TMAC), the inclusion particles are Mn and S The Cu-added steel sheet according to any one of claims 1 to 4, wherein the Cu component is not contained in the inclusions.